Impedance control coupling and decoupling system



Sept. 7, 1954 .c. YOUNG 2,538,731

' IMPEDANCE CONTROL COUPLING AND DECOUPLING SYSTEM Original Filed March 29, 1940 5 TO ANTENNA BALANCED DIODES RECEIVER TRANSMITTER swam M LEO C. YOUNG ATTO RNEY Patented Sept. 7, 1954 IMPEDANCE CONTROL COUPLING AND DECOUPLING SYSTEM Leo C. Young, Washington, D. C., assignor to Radar Incorporated, Washington, D. 0., a corporation of Delaware Original application March 29, 1940, Serial No. 326,640. Divided and this application February 13, 1948, Serial No. 8,264

2 Claims. (Cl. 333 -13) (Granted under Title 35, U. S. Code (1952),

sec. 266) This application is a division of application Serial Number 326,640 filed March 29, 1940.

This invention relates to non-linear filter elements and particularly to a filter element adapted, to act as a high impedance shunt across a transmission line at low potentials and as a low impedance shunt for high potentials exceeding a predetermined value.

It is accordingly a primary object of this invention to provide a transmission line shunt which acts as a high impedance for low potential line conditions and as a low impedance when the line potentials exceed a predetermined value.

The invention comprises a quarter-wave line section, shorted at one end, to which a transmission line may be connected at an intermediate point. A discharge path is provided across the other end of the line. The discharge path may be a gas discharge tube.

By transformer action of the quarter-wave section, the voltage across the discharge path is of greater value than that carried by the line. When the increased voltage reaches or exceeds the discharge potential, the path becomes conductive and line section is then effectively short circuited at both ends. Consequently, for high line potentials a low impedance shunt is provided.

The invention will be described in connection with an exemplary utilization circuit disclosed in application Serial No. 326,640 mentioned above. In the drawing, the figure shows the invention employed in a radio transmitting and receiving system.

In the figure, a transmitter is diagrammatically represented by tubes I and 2 having their anodes 3 and 4 coupled to antenna leads 5 and B which are grounded at 1. Shorting bar 8 of a quarterwave parallel resonant line section 9 is grounded at and the two parallel members H and [2 thereof are connected to antenna leads and 5 by leads I3 and 14. Elements l5 and I6 aiiord means for coupling line l3-l4 to the two conductors II and I2 of the quarter-wave line section 9. The line section 9 is connected to receiver input grid I! by a suitable transformer [8.

It is well known that a voltage antinode exists at the end of a quarter-wave resonant line remote from the shorting bar and. I have therefore provided the balanced diode [9 with an anode thereof respectively connected to each of the members II and I2 of resonant line 9. The diod l9 ignites and passes current at and above a predetermined voltage and thus provides a low impedance shunt across line I3l4. This destroys the impedance match of the receiver through to lines 5 and 6 when the voltage impressed on diode I9 is swung above the predetermined limit during transmission. As disclosed in application Serial No. 326,640, line l3-l4 may be a quarterwave line acting as an impedance inverting deviceand serving to transfer a short circuit at the resonant line 9 to a virtual open circuit across the transmission line 5-6. During the reception of energy, with transmitter tubes l and 2 inoperative, the receiver is effectively matched through to the antenna and consequently efliciently absorbs the energy from the antenna. Under these conditions the quarter-wave section 9 acts as a high impedance shunt across line 13-44.

The invention herein described and claimed may be used and/or manufactured by or for the Government of the United States of America for governmental purpose without the payment of any royalties thereon or therefor.

What is claimed is:

1. A filter element including a two conductor line section having a length equal to one quarter wavelength at a predetermined operating frequency and having a discharge path connected across one end, said line being short-circuited at the other end and means for coupling a transmission line across said two conductor line section at a predetermined intermediate point, said discharge path causing said line section to act as a high impedance shunt across said transmission line at potentials below the discharge potential of said path and as a low impedance shunt across the said transmission line for potentials above the discharge potential of said path.

2. A filter element including a two conductor line section having a length equal to one quarter wave-length at a predetermined operating frequency and having a gas discharge tube connected across one end, said line being short-circuited at the other end and means for coupling a transmission line across said two conductor line section at a predetermined intermediate point, said discharge tube causing said line section to act as a high impedance shunt across said transmission line at potentials below the discharge potential of said tube and as a low impedance shunt across the said transmission line for potentials above the discharge potential of said tube.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,035,958 Girardeau Aug. 20, 1912 1,872,398 Brown Aug. 16, 1932 FOREIGN PATENTS Number Country Date 358,917 Great Britain Oct. 14, 1931 

